1. Field of the Invention
The present invention relates to a pickup movement device in which one of a plurality of electromagnetic driving coils is adapted to switch for use in the detection of the movement and movement speed of a pickup.
2. Description of the Related Art
In recent years, there has been available an optical record reproducing device (hereinafter referred to as an optical disk device) which is capable of recording information optically on an optical disk by forming a train of pits or the like thereon. The optical disk device is capable of reproducing the recorded information by receiving light reflected from a recorded train of pits, when the optical recording medium (hereinafter referred to as an optical disk) is irradiated with light beams condensed by an optical pickup.
In the prior art where a light beam is moved to a target track with respect to the above-mentioned optical disk, a method has been adopted such that an external scale is used in a linear motor and an optical pickup is moved to the vicinity of the target track by using the information obtained from this external scale, after which tracking is carried out to confirm a moved track address and then tracking jumps to the target track.
In recent years, as disclosed in Japanese Patent Publication No. 58-91536, a means (referred to as direct access means) which directly moves to a target track by counting track error signals without using an external scale has been used, aiding in reductions in access time and in cost.
The above-mentioned direct access means has the following problems.
When a vibration is applied to the optical pickup, the movement speed cannot be distinguished, thereby causing a runaway.
That is, when an optical disk is driven to rotate, generally, an eccentricity cannot be avoided.
If the track movement speed (track crossing speed) is made higher so as to render the influence of the speed of eccentricity (the component of the speed in a track crosswise direction) small, the influence of the eccentricity can be avoided. However, when the track movement speed (with respect to the optical disk) becomes relatively small due to a variation, a controller controls so as to make the track movement speed higher, possibly causing a runaway. If the controller is placed in a defocus state because of the variation and a track error signal cannot be detected, the controller controls so as to make the movement speed higher, and runaway may possibly occur.
The track movement speed becomes relatively lower due to the variation and at that time a situation can arise in which a light beam crosses a track in a reverse direction because of the eccentricity. In this case, the correct number of track movements cannot be obtained even if the track error signals are counted, and therefore, prompt track access cannot be made.
On the other hand, Japanese Patent Publication No. 51-99006 discloses an optical disk device in which a coil is wound around each of the ends of a tubular member and one of the coils is used in a driving coil, another coil being used for speed detection.
Japanese Utility Model Examined Publication No. 58-9510 (Japanese Utility Model Unexamined Publication No. 54-152916) discloses a linear motor provided with a driving coil in which the same poles of two magnets are connected to each other by yokes and a driving coil is movably wound on one of the yokes, and provided with a movement speed detection coil integrally connected to this driving coil and movably wound on the other yoke.
Further, Japanese Patent Publication No. 1-112576 discloses an optical disk device in which a magnetic shield plate is provided between a driving coil and a speed detection coil.
When a speed detection coil is provided and the speed of a pickup is detected as in the second and fourth publications, a speed detection coil must be provided in addition to a driving coil. Problems arise in that manufacturing cost is increased and the pickup becomes heavy.